1. Field of the Invention
The present invention relates to a peak signal detecting device for detecting a peak of an input signal.
2. Description of the Prior Art
FIG. 8 is a block diagram showing a system architecture of a conventional peak signal detecting device for detecting a peak of an input signal, such as a magnetic disc reading signal and the like. FIG. 9 is a waveform diagram showing various signals in the peak signal detecting device. As shown in FIG. 8, a reading signal S0 (see FIG. 9) is applied through an input terminal 7 to a differentiating circuit 1 and level slice circuit 3.
The differentiating circuit 1 differentiates the reading signal S0 to output a differentiated signal S1 (see FIG. 9) to a zero cross detecting circuit 2. The zero cross detecting circuit 2 takes in the differentiated signal S1, and when detecting a time when the differentiated signal S1 reaches a zero level (a time when it crosses the zero level) ordinarily at Low level, that is, a time when an inclination of the reading signal S0 becomes 0, it outputs a zero cross signal S2 (see FIG. 9) which becomes a pulse at High level for a specific period of time, to the gate circuit 4.
On the other hand, the level slice circuit 3 outputs a level slice signal S3 (see FIG. 9) which turns to High/Low depending upon whether an absolute value of the reading signal S0 is more/less than a specified threshold value VT1, to the gate circuit 4.
The gate circuit 4 receives the zero cross signal S2 and level slice signal S3 to output a gate signal S4 (see FIG. 9) which is a conjunction of the signals S2 and S3 through an output terminal 8 to the outside. Thus, the gate signal S4 reaches the High level when the differentiated signal S1 is 0 and the absolute value of the reading signal S0 is eual to or more than VT1, while the gate signal S4 is at the Low level at a time when the reading signal S0 is near zero level with an inclination 0. As a result, the gate signal S4 reaches the High level in correspondence with a time when the reading signal S0 reaches its peak, and hence, detecting the High level of the gate signal S4 allows the peak of the reading signal S0 to be detected.
However, in the conventional peak signal detecting device, when, as shown at a time t1 in FIG. 10, a noise NZ is caused at a level over the threshold value VT1 of the level slicing circuit 3 and a false extreme point is generated in the reading signal S0, the zero cross signal S2 turns to the High level while the level slice signal S3 also turns to the High level, and the gate signal S4 turns to the High level. Hence, a generating point of the noise NZ may be erroneously detected as a time of the peak, and thus, there arises the problem that an accuracy in detecting a peak time is degraded.